What made her draw that line though?

The "two passes" thing is real but the reason isn't the coffee, it's that you're giving the ink time to dry so your hand doesn't drag through wet lines. Pencil first helps too, sure, but the bigger fix is just slowing down on pass two. I do mine the same way with a ruler and a fine liner, and honestly the pencil part barely matters once you get the feel for it, I've skipped it plenty of times and my grids still come out clean. What actually saved my spreads was drawing the boxes on a separate scrap page first so I'm not wrecking the real one when I mess up. So yeah, cool tip from that barista, just don't give the coffee credit it doesn't deserve lol.

Man, I gotta disagree on the 80% dry thing. Fine hair sure, dry cutting shows you the natural fall and you can see where it wants to sit, that part makes total sense. But for thick or curly clients you're rolling the dice, wet hair stretches and springs back, so a dry cut can end up shorter than you planned once they wash it at home. I do a hybrid, consult and rough shape dry, then finish wet so the lines are clean and I know exactly what's coming off. The shampoo thing is just habit for most people, I tell them straight that I can see their hair better dry and they usually come around after one cut.